1. Field of the Invention
The invention is directed to using an operator controlled non-linear potentiometer to adjust a valve regulating the flow of heated fluid to an operator cab of a vehicle.
2. Description of the Prior Art
Vehicles are provided with operator cabs for housing the operator controlling the vehicle. The operator cab is typically provided with a heating system so the vehicle can be operated in cold conditions. The vehicle is powered by an internal combustion engine. A portion of the heat created by the combustion process is used to heat a fluid that is directed through a supply line to a heat exchanger in communication with the interior of the operator cab. To control the heat output of the heat exchanger, a valve is positioned in the supply line to regulate the flow of heated fluid to the heat exchanger. In the past, these valves have been controlled by an electrical actuator. The electrical actuator in turn is electrically coupled to a conventional rotary potentiometer. The operator by adjusts the flow of heated fluid to the heat exchanger by rotating the potentiometer to a selected heating position. In this design the position of the potentiometer is directly related to the position of the valve regulating the flow of hearted fluid. For example, if the rotary potentiometer is rotated through ten percent of its control arc the valve would be opened ten percent. However valve position is not proportional to heat output at the heat exchanger in the operator cab. For example it has been found that if a conventional potentiometer had a 270 degree control arc the heat output would max out at approximately 120 degrees of rotation. Therefore the operator's effective control of the heat output in the cab would be limited to the first 120 degrees.
To overcome this problem some vehicles are provided with automatic temperature control systems having a feedback loop to the control the valve. These systems are more expensive to manufacture and maintain.